Air flow characteristics in granular biofilter media

Pressure drop (ΔP) as a function of air velocity (V) is a key parameter controlling air cleaning biofilter cost efficiency. At present the V-ΔP relationship in biofilter materials must generally be determined experimentally, as no universal link between the V-ΔP relationship and material physical properties have been established. The objective of this study was, therefore, to investigate the link between the V-ΔP relationship, material particle size distribution, and wetting conditions for a common biofilter medium, Leca. Measurements of V-ΔP was carried out for 36 different Leca particle size fractions with different mean particle diameter (D_m) and particle size range (R) under both dry and wet conditions. Measurements showed that increasing D_m and decreasing R together with wetted conditions in the filter generally resulted in decreasing ΔP for the same V. A set of expressions allowing for accurate estimation of the V-ΔP relationship based on D_m, R. and wetting conditions were established, enabling reliable estimation of filter pressure drop (and operation costs) in Leca and similar granular materials.